The present invention relates to data network communications and in particular to a switching point of a data network having a plurality of network access servers.
The conventional way for a home user of a personal computer (PC) to access the Internet is to set up a telephone call, via his telephone operator, to an Internet service provider. The service provider allocates an Internet address to the PC (xe2x80x9csubscriber terminalxe2x80x9d) for the duration of a session and acts as a protocol converter for data transmitted between the Internet and the subscriber terminal.
More recently, it has been proposed to combine the functionality of the Internet service provider into certain exchanges of the telephone network. An advantage of this is that the subscriber need only receive a single bill for both telephone calls and Internet access.
Exchanges provided with this facility are accessed by subscribers dialling a predefined access number. The exchanges contain xe2x80x9cintelligencexe2x80x9d which enables them to recognise that a call received to this number is an Internet access request. In response, the exchange provides a connection between the subscriber terminal and the Internet via one of a number of so-called Internet Access Servers (IASs)xe2x80x94alternatively known as Network Access Servers (NASs).
The connection between the subscriber terminal and the IAS is a circuit switched connection, i.e. occupying reserved bandwidth, and utilises a Point-to-Point Protocol (PPP) such as is defined in RFC 1661. The reserved bandwidth comprises one Integrated Services Digital Network (ISDN) traffic channel (B-channel) providing a bandwidth of 64 Kbits/sec.
The number of IASs provided at an exchange determines the Internet access capacity of the exchange. However, using PPP, the bandwidth which can be accessed by an individual subscriber is limited to 64 Kbits/sec (i.e. one ISDN B-channel).
A Multilink PPP (RFC 1990 (1717)(1934)) has been proposed in order to provide further transmission bandwidth to subscriber terminals. This protocol uses a combination of two or more connections to provide a single larger channel. Considering for example the situation where the subscriber line to the exchange makes use of the Integrated Services Digital Network (ISDN) user-network interface, it is possible to make use of both of the communication B-channels available on the subscriber line for Internet access.
This works satisfactorily as long as all of the individual B-channels making up the multilink channel terminate at the same IAS. However, Multilink PPP cannot operate where individual B-channels are provided via different IAS, as the order of data packets sent between the Internet and the subscriber terminal may be lost due to variations in the transmission delays between different B-channels. Also, IP does not provide a mechanism whereby packets having the same IP address can be sent via different IASs.
It often transpires that when a low bandwidth access has been provided to a subscriber terminal, and that terminal subsequently requests additional bandwidth (i.e. using Multilink PPP), the allocated IAS cannot provide that bandwidth and multilink access cannot therefore be provided. Whilst it is possible to always reserve spare capacity on an IAS for a subscriber terminal already allocated a channel on that IAS, this may be wasteful of bandwidth resources.
This problem could be alleviated by increasing the capacity provided by an IAS. However, capacity is a function of processor power, power consumption, board size, etc. and cannot easily be achieved. An alternative solution which has been proposed involves connecting several IASs (which are usually provided in the form of printed circuit boards loaded into racks of an exchange) to a common multilane cell bus. The disadvantage of this solution is that the number of IAS which can be connected together in this way is limited (due to limits imposed by the capacity of the common bus) and also that a new inter-IAS communication protocol is required.
It is noted that similar problems arise in connecting a subscriber terminal to other types of data networks via data network access servers, where it is desired to utilise a multilink PPP.
It is an object of the present invention to overcome or at least mitigate the above noted disadvantages. In particular, it is an object of the present invention to provide a switching point for connecting a terminal to a data network using multilink point-to-point protocol.
According to a first aspect of the present invention there is provided a method of connecting a terminal to a data network, wherein the connection is made through a switching point having a plurality of data network access servers coupled to the data network, the method comprising:
in response to an access request received from the terminal, determining whether or not an active connection currently exists for that terminal over one of said data network access servers;
if an active connection does not currently exist, allocating to the terminal, transmission bandwidth on one of the data network access servers; and
if an active connection does exist, identifying the data network access server on which transmission bandwidth is allocated to the terminal, allocating additional bandwidth to the terminal on that data network access server if available or, if not available, transferring the active connection to a second data network access server on which sufficient bandwidth is available.
By ensuring that transmission bandwidth for a given terminal is always allocated on a single data network access server, embodiments of the present invention ensure that multilink point-to-point protocol can be used as the communication protocol between the terminal and the data network.
In certain embodiments of the invention, the data network is a wide area network such as the Internet, in which case the data network access servers are Internet access servers.
The switching point at which the data network access servers are provided may be an exchange of a telephone network in which case the terminal may be connected to the exchange via a telephone line of the telephone network or via a wireless telephone communication channel.
The terminal may be connected to a further data network, e.g. a Local Area Network (LAN), and through that network to the switching point.
The terminal may be a subscriber terminal on which is run a user application, e.g. a Web browser. Alternatively, the terminal may provide a routing functionality for other, end-user terminals connected to the first mentioned terminal by a Local Area Network (LAN) or a Wide Area Network (WAN).
According to a second aspect of the present invention there is provided apparatus for connecting a terminal to a data network, the apparatus comprising a switching point having a plurality of data network access servers coupled in parallel to the data network, and processing means associated with the switching point, the processing means being arranged, in response to an access request received from the terminal, to:
determine whether or not an active connection currently exists for that terminal over one of said data network access servers;
if an active connection does not currently exist, to allocate to the terminal transmission bandwidth on one of the data network access servers; and
if an active connection does exist, to identify the data network access server on which transmission bandwidth is allocated to the terminal, and to allocate additional bandwidth to the terminal on that data network access server if available or, if not available, to transfer the active connection to a second data network access server on which sufficient bandwidth is available.
In one embodiment of the above second aspect of the present invention, the data network is the Internet and said data network access servers are Internet access servers. More preferably, the switching point is an exchange of a telephone network, and the network comprises a telephone line, or wireless radio telephone link, coupling the terminal to the exchange.